Method for copper-plating or bronze-plating an object and liquid mixtures therefor

ABSTRACT

The invention relates to an aqueous concentrate which is stable with respect to freezing and defrosting and which contains at least one water-soluble or water-dispersible copper compound and, optionally, also a water-soluble or water-dispersible tin compound for use in a diluted state as a bath for the currentless copper plating or bronze plating of objects, especially metal objects such as iron or steel wires, characterized in that it contains at least one complexed water-soluble or water-dispersed copper compound. The invention also relates to an aqueous bath which contains at least one aqueous or water-dispersible copper compound and, optionally, a water-soluble or water-dispersible tin compound for the currentless copper plating of objects in addition to at least one brightening agent and which has an adjusted pH value of less than 2.5. The invention also relates to a method for currentless copper plating or bronze plating of an object, especially a metallic object.

This is a §371 of PCT/EP03/03427 filed Apr. 2, 2003, which claimspriority from German 102 14 859.7 filed Apr. 4, 2002, each of which arehereby incorporated by reference in their entirety

The present invention relates to a process for the currentless coppering(copper coating) or bronzing (bronze coating) of an object, inparticular a metallic object, more particularly an object of a ferrousmaterial, above all an iron wire, steel wire or a wire-containingaggregate such as for example a wire mesh, with an aqueous bathcontaining dissolved copper.

The object of coppering or bronzing is not only to protect the surfacesof the objects to be coated by means of the copper-containing coatingagainst corrosion, but also to form a coating that is as uniform, shinyand adherent as possible. In this connection a peel resistance(adherence) on bending a wire for example as well as a layer weightroughly in the range from 0.8 to 24 g/m², in particular in the rangefrom 1 to 18 g/m², are desired. The coppering or bronzing bath should besuitable for currentless metallising.

Up to now coppering baths for this purpose are known in which the bathis prepared using a pulverulent copper-rich concentrate, water andsulfuric acid. The baths may for example contain apart from coppersulfate, also sodium chloride, a magnesium salt, a brightening agent andoptionally further additives. The powder at the same time offers thepossibility of holding comparatively high copper contents in theconcentrate and thus of transporting comparatively low weights.

Water and sulfuric acid are normally available in situ or can beobtained nearby. Such pulverulent concentrates often have a coppercontent in the range from 12 to 22 wt. % Cu. The concentrates are verysensitive to moisture on account of the high content of copper sulfate,and their quality depends in particular on the freedom from or on thenature and amount of the impurities and/or additives. On account of thesensitivity to moisture and the chemical reactions occurring in thepowder as a result of the moisture, the storage life of the pulverulentconcentrates is often limited. Changes are initially manifested by agreen colouration and subsequently end in agglomerations. Thepulverulent concentrate, which is often stored for months, is made up insitu with water and sulfuric acid before coppering, and the copperingbath is in many cases maintained ready for use over several weeks and isreplenished as necessary. The pulverulent concentrate often requiresprolonged stirring or agitation and possibly heating to a slightlyelevated temperature, such as for example up to 60° C. Since thecoppering bath is however normally kept and used in premises that can beheated as necessary, there is normally no need for the bath to be stablewith regard to freezing and thawing. Furthermore the requirements asregards the industrial use also of concentrates and baths for copperingare becoming increasingly stringent.

On account of the often months-long storage and the in some cases fairlylong transportation of concentrates to the currentless coppering andbronzing site, there was a need to develop a concentrate that can bestored if possible for several months and that can be transportedwithout any problem in various climatic regions. In the case of a liquidconcentrate a concentrate has to be developed that also does not causeany problems as regards freezing and thawing, since once copperingsolutions have been frozen they no longer independently form homogeneoussolutions. Also, an addition of antifreeze agents does not help sincethe salts precipitate in any case and form a floor sediment. Accordinglyin practice virtually only pulverulent concentrates or, in exceptionalcases, two-component concentrates are produced with copper sulfatesolution as well as with a separately stored liquid mixture ofbrightening agent and other sensitive liquids. Up to now no liquidconcentrate for currentless coppering or bronzing is known to theApplicant that contains all or virtually all the components needed forcoppering or bronzing.

In addition the object existed of providing a concentrate and a processfor currentless coppering or bronzing that is as environmentallyfriendly as possible and that moreover has as safe a pH value aspossible. These concentrates should in addition be able to be usedeasily, without complications and efficiently for the coppering orbronzing. The concentrate should have as high a copper content aspossible. The bath prepared from the concentrate inter alia by dilutionshould form high-gloss, solid, firmly adhering copper coatings. It wouldbe advantageous if this concentrate were to contain all the componentsfor the currentless coppering or bronzing.

It has been established that an aqueous copper-rich concentrate in whicha large part of the copper content is present in complexed form canexist as a solid homogeneous mass below the freezing point and canrapidly re-form into a homogeneous aqueous mixture on thawing, withouthaving to be stirred or agitated.

This object is achieved with an aqueous concentrate that is stable onfreezing and thawing that contains at least one water-soluble orwater-dispersible copper compound and optionally also a water-soluble orwater-dispersible tin compound for use in the diluted state as a bathfor the currentless coppering or bronzing of objects, in particularmetallic objects such as for example iron or steel wires, which ischaracterized in that it contains at least one complexed water-solubleor water-dispersed copper compound.

Preferably all compounds present in the concentrate are dissolved ordispersed in water. The complexing agent may be contained instoichiometric amount, in a sub-stoichiometric amount or in excess.Preferably the concentrate contains a basic copper carbonate or at leastone compound formed therefrom by complexing with a complex-formingagent. On account of the complexing a high copper content can bemaintained in the solution without precipitation occurring.

The mixture may be repeatedly frozen at low temperatures down to atleast −14° C. and may be thawed without the quality of the mixture, inparticular the quality of the coppering bath prepared therefrom, beingadversely affected. This mixture normally serves as a concentrate thatcan be transported as a liquid product and that by dilution andoptionally by addition of individual additives can be made up into acoppering bath, or at the same time can be used as a replenishmentsolution to replenish the copper content and the contents of the furthercomponents of such a bath, in particular a coppering bath.

This mixture is according to the knowledge of the Applicant the firstproduct that can durably be stored as a non-pulverulent Cu-containingconcentrate for at least one month and possibly even several years undernormal conditions, and that can withstand a cold stability test at −14°C. for at least one week without any problem. It is therefore the firstnon-pulverulent product that can be transported overseas and used therewithout any problem since pulverulent copper-rich concentrates arealways extremely hygroscopic and undergo chemical changes relativelyquickly and markedly. A suitable alternative to bronzing is providedwith a tin content of at least 0.01 g/l Sn. The tin content ispreferably 0.5 to 20 wt. % of the sum total of all metals or metal ionsthat are required for the alloy composition of the bronze, and is inparticular 1 to 25 wt. % and preferably 2 to 15 wt. % of the amount ofcopper employed.

The bath is preferably largely or wholly free of halides and/or anions,in particular halides and/or anions such as chloride and/or nitrate,though halides and/or anions may also be entrained from other baths.

The concentrate according to the invention is preferably free or largelyfree of cyanides, diphosphates, phosphates, sulfamates, borates,bromides, fluorides, fluoroborates and/or iodides. The substantial orcomplete freedom from these and possibly also other anions issignificant in order that the anions do not lead to the precipitation ofsalts when the aqueous solution is cooled below the freezing point andaccordingly do not affect the stability as regards freezing and thawing.This is due to the fact that hydrated copper sulfate can precipitateonly in the presence of anions. Preferably these anions and heavy metalsare not intentionally added, apart from copper, possibly apart from tinand possibly also apart from further alloying constituents of thecopper-rich coating to be formed. Preferably the concentrate and/or bathaccording to the invention is also free or largely free of other heavymetals such as for example cadmium, gold, cobalt, manganese, nickel,silver and/or further steel-finishing additives, in which connectioncontents of heavy metals that are dissolved out from the metallicmaterial to be coated and which derive from the raw materials or areentrained from other baths often cannot be avoided. In the case ofparticularly high amounts of complexed compounds it is preferred to addthe complexing agent in the preparation of the concentrate in anapproximately stoichiometric ratio to the content of copper and possiblyalso tin or even in a hyper-stoichiometric amount (approximately of theorder of magnitude of ca. 1:1), particularly preferably in the rangefrom (0.9-1.2):1, most particularly preferably in the range from(0.96-1.10):1 and above all in the range from (0.99-1.05):1.

The concentrate according to the invention should con-tain at least 40wt. % of the contained copper compounds in complexed form. Preferably atleast 50 wt. % of the contained copper compounds, more preferably atleast 60 wt. %, most particularly preferably at least 70 wt. %, inparticular at least 80 wt. %, more particularly preferably at least 90wt. % and above all at least 95 wt. % of the contained copper compoundsare in complexed form. Preferably the copper compounds and possibly alsotin compounds are largely or wholly complexed. Other alloyingconstituents may also be largely or wholly complexed. In addition, atleast one tin compound may also be present in complexed form. Apart fromthe copper complex compounds, possibly preferably hydrated coppersulfate and/or similar copper or tin compounds may be included.

The concentrate may contain at least one copper compound that is atleast partially complexed with a complex-forming agent based on at leastone complexing monohydroxycarboxylic, dihydroxycarboxylic,trihydroxycarboxylic and/or polyhydroxycarboxylic acid, phosphonic acid,diphosphonic acid and/or at least one of their derivatives. Thecomplex-forming agent is preferably based on citric acid, gluconic acid,lactic acid, tartaric acid, phosphonic acid, diphosphonic acid,chemically related acids and/or one of their derivatives. The additionof the at least one complex-forming agent may take place inter alia inthe form of an acid, salt and/or organic compound, in particular of analkali metal, alkaline earth metal and/or ammonium. The complexed copperand/or tin compounds are preferably citrates, gluconates, lactates,tartrates, phosphonates, diphosphonates and/or their derivatives orchemically related compounds.

The concentrate is stable to freezing and thawing preferably down to atleast −8° C. In particular it is stable to freezing and thawing down toat least −14° C., preferably down to at least −20° C. and particularlypreferably down to at least −25° C. Stability to freezing and thawingwithin the context of the present invention means that the aqueousmixture can be repeatedly cooled to temperatures down to for example−20° C., for example under normal storage conditions such as in the openair in Winter, and that the mixture is ready for use after heating totemperatures significantly above the freezing point of the aqueousmixture even without stirring or agitation and/or without prolongedwaiting until all the constituents have dissolved to form a homogeneoussolution. In the fresh state the bath is dark blue, at a certain ironcontent is greenish, and after long use is, depending on thecircumstances, brownish-black on account of the dissolved iron. In thecase of high contents of complexed compounds instead of salts in theaqueous mixture, scarcely any such floor sediment or no floor sedimentat all is formed and there is scarcely any or no differentiation inregions with high and low metal contents. Accordingly the bath producedfrom the concentrate by dilution may also be stable to freezing andthawing, though not necessarily so.

The concentrate preferably has a copper content in the range from 3 to200 g/l Cu, more preferably at least 15 g/l, particularly preferably atleast 30 g/l, most particularly preferably at least 60 g/l, orpreferably at most 160 g/l, particularly preferably at most 130 g/l andmost particularly preferably at most 110 g/l.

In principle a pH value may be chosen in a wide pH range. Advantageouslythe concentrate is adjusted to a pH value in the range from 4 to 11.Preferably the concentrate has a pH value in the range from 5 to 10,particularly preferably in the range from 6 to 9, and most particularlypreferably in the range from 7 to 8. The adjustment may be made interalia with at least one base such as for example NaOH, KOH and NH₄OHand/or with at least one amine. If the concentrate has a pH of about 7,it may be termed as dermatologically neutral.

The concentrate advantageously contains at least one copper compoundthat is at least partially complexed with a complexing agent based on atleast one monohydroxycarboxylic, dihydroxycarboxylic,trihydroxycarboxylic and/or polyhydroxycarboxylic acid, phosphonic acid,diphosphonic acid and/or chemically related compound and/or at least oneof their derivatives.

The object of the present invention is also achieved with an aqueousbath that contains at least one water-soluble or water-dispersiblecopper compound and also a water-soluble or water-dispersible tincompound for the currentless coppering or bronzing of objects, inparticular metallic objects such as for example iron-containing wires,as well as at least one complexed copper compound and at least onebrightening agent, the said bath being adjusted to a pH value of lessthan 2.5.

Preferably all compounds present in the bath are dissolved or dispersedin water. An addition of tin and optionally generally minor amounts ofother alloying constituents may advantageously be made in the form ofwater-soluble or water-dispersed compounds such as tin hydroxide, tincarbonate and/or at least one organotin compound such as for example atleast one tin alcoholate or similar compounds of the further alloyingconstituents that are possibly used in the preparation of the bath, i.e.starting from the concentrate. The amount of tin added to the bath mayin particular be in the range from 0.03 to 8 g/l Sn. The concentrateand/or bath according to the invention is preferably free or largelyfree of cyanides, diphosphates, phosphates, sulfamates, borates,bromides, fluorides, fluoroborates and/or iodides. The bath may howevercontain halide, in particular halide entrained from the upstreampickling baths. Preferably these anions and heavy metals, apart fromcopper, tin and possibly further alloying constituents of thecopper-rich coating that is to be formed, are not added intentionally.Preferably the concentrate and/or bath according to the invention isfree or largely free of other heavy metals such as for example cadmium,gold, cobalt, manganese, nickel, silver and/or further steel-finishingadditives, in which connection contents of heavy metals that aredissolved out from the metallic material to be coated, that are derivedfrom the raw materials or that are entrained from other baths, oftencannot be avoided or cannot be sufficiently avoided.

In the aqueous bath at least 40 wt. % of the contained copper compoundsmay be complexed, preferably at least 50 wt. %, more preferably at least60 wt. %, most particularly preferably at least 70 wt. %, in particularat least 80 wt. %, most particularly preferably at least 90 wt. % andabove all at least 95 wt. %. Furthermore at least one tin compound mayalso be complexed. Apart from the copper complex compounds, hydratedcopper sulfate, copper chloride and/or similar copper or tin compoundsmay for example be contained. Preferably the bath contains a basiccopper carbonate or the at least one compound formed therefrom bycomplexing.

The bath may advantageously have a copper content in the range from 0.05to 120 g/l. Preferably the copper content of the bath is at least 0.1g/l, particularly preferably at least 0.2 g/l, most particularlypreferably at least 0.4 g/l, or preferably at most 100 g/l, particularlypreferably at most 70 g/l and most particularly preferably at most 45g/l. For the coppering of wires copper contents of the bath above all inthe range from 0.5 to 35 g/l Cu are suitable for throughflow processesas well as for dipping processes, in particular contents of about 22 to25 g/l.

The bath may have a dissolved iron content of up to at least 90 g/l oreven up to at least 110 g/l Fe²⁺, and despite this may in principle becapable of use. The bath may in certain circumstances be operated withan even higher dissolved iron content.

The bath may contain at least one copper compound that is at leastpartially complexed with a complex-forming agent based on at least onecomplexing monohydroxy-carboxylic, dihydroxycarboxylic,trihydroxycarboxylic and/or polyhydroxycarboxylic acid, phosphonic acid,diphosphonic acid and/or at least one of their derivatives. Preferablythe complex-forming agent is one containing 4 to 12 carbon atoms, inparticular citric acid, gluconic acid, lactic acid, tartaric acid,phosphonic acid, diphosphonic acid and/or one of their derivatives, inparticular at least one alkali metal, ammonium or alkaline earth metalcitrate, alkali metal, ammonium or alkaline earth metal gluconate,alkali metal, ammonium or alkaline earth metal acetate and/or alkalimetal, ammonium or alkaline earth metal tartrate or analogousphosphonates and/or diphosphonates. The addition of the at least onecomplex-forming agent may take place inter alia in the form of an acid,salt and/or organic compound of an alkali metal, alkaline earth metaland/or ammonium. Part of the iron content taken up in the bath islikewise complexed in the process according to the invention. Thecomplexed copper, tin and/or iron compounds are preferably citrates,gluconates, lactates, tartrates, phosphonates, diphosphonates and/ortheir derivatives. It was found from experience that an excessive amountof the complex-forming agent and of the brightening agent does not havea damaging effect.

The bath may have a content of reacted or unreacted complex-formingagent in the range from 0.1 to 400 g/l, jointly calculated as unreactedcomplex-forming agent. Preferably the content is at least 1 g/l,particularly preferably at least 2 g/l, most particularly preferably atleast 4 g/l, or preferably at most 150 g/l, particularly preferably atmost 100 g/l and most particularly preferably at most 60 g/l.

The bath may have a content of at least one brightening agent, inparticular a brightening agent with a content of amide, amine, imide,imine, polymeric aminoalcohol, polyamide, polyamine, polyimide,polyimidazoline and/or polyimine. Advantageously a brightening agent isselected that is stable in the pH range from 4 to 11 and that functionsefficiently. Preferably the brightening agent contains at least onecompound based on dimethylamine, hexamethyleneamine, propylamine orcorresponding imine, amide or imide and/or oxirane, particularlypreferably polymeric compounds based on the latter, above all polymericcompounds based on amine with epichlorohydrin, in particular those withpropylamines and/or tetramines, most particularly preferably polymericcompounds based on dimethylaminopropylamine and/orhexamethylenetetramine with epichlorohydrin.

The bath may have a content of at least one brightening agent in therange from 0.05 to 20 g/l. Preferably its content is at least 0.2 g/l,particularly preferably at least 0.5 g/l, most particularly preferablyat least 1 g/l, or preferably at most 12 g/l, particularly preferably atmost 8 g/l and most particularly preferably at most 4 g/l.

The bath may also have a content of at least one pickling agent, inparticular at least one halide of an alkali metal, alkaline earth metaland/or of ammonium and/or at least one acid, in particular at least onemineral acid. The pickling agent is preferably an alkali metal chloride,alkali metal bromide or alkali metal fluoride such as for example KCl,NaCl, NaBr, NaF, and/or at least one acid such as for examplehydrochloric acid and/or hydrofluoric acid. Preferably pickling agent isadded in an amount, generally a minor amount, such that a weakadditional pickling effect is produced that facilitates the dissolutionof the baser metal ions from the surface. It is not at all necessary toadd at least one pickling agent, though the use thereof is advisable ifthe surfaces are particularly passive and it is also scarcely feasibleto carry out a sulfuric acid pickling.

The bath may be adjusted to a pH value in the range less than 2.5.Preferably the bath has a pH value in the range up to 2.0, particularlypreferably a range around 1.0 or at most 1.0. The adjustment mayadvantageously be carried out inter alia with acids such as for examplesulfuric acid and/or other sulfur-containing acids.

The bath may contain at least one lubricating additive that iswater-soluble and/or water-dispersible, and/or that allows at least onelubricating additive to separate out during the coppering or bronzing.The lubricating additive should for example improve the frictionalbehaviour in wire manufacture and reduce the cutting action of the wire,on for example plastics elements; it may be a typical lubricant, but mayhowever also in each case be at least one high molecular weightpolyglycol, an ester, a high molecular weight surfactant, a highmolecular weight fatty acid or one of their derivatives, such as forexample at least one fatty acid ester, in particular at least one fattyacid polyglycol ester and/or fatty acid polyglycol ether.

The bath may be stable to freezing and thawing down to at least −8° C.Preferably it is stable to freezing and thawing down to at least −14°C., particularly preferably down to at least −20° C. and mostparticularly preferably down to at least −25° C. The freezing andthawing stability is not necessary for a bath that is normally used inpremises that can be heated. Also, the freezing and thawing stability ofthe bath depends to a large extent on the substantial or completefreedom from anions apart from sulfate.

In principle the bath can be prepared from the concentrate according tothe invention by dilution with water and optionally under the additionof in each case at least one acid, salt, brightening agent, picklingagent and/or further additive.

The object of the present invention is furthermore achieved by a processfor the currentless coppering or bronzing of an object, in particular ametallic object, with an aqueous bath according to the invention that isformulated from a concentrate according to the invention by addition ofwater and if necessary in each case by addition of at least one acid,salt, brightening agent, pickling agent and/or further additive to theready-for-use aqueous bath for the coppering or bronzing.

The dilution of the concentrate to form the bath is preferably carriedout at dilution factors in the range from 2 to 50, particularlypreferably in the range from 4 to 30, most particularly preferably inthe range from 6 to 20. In this connection the pH of the bath may beadjusted to values around or below 1.0 and maintained in this range ofvalues. In the coppering of steel wires a treatment time for copperingby dipping of 30 to 180 sec. was hitherto customary. Preferably theobject to be metallised by dipping is contacted with the bath liquid fora time ranging from 0.1 to 8 minutes, and in throughflow metallising fora time ranging from 0.1 to 30 seconds. In particular metallising iscarried out at a bath temperature in the range from 5° to 80° C.,preferably in the range from 10° to 70° C., in the case of dippingespecially in the range from 15° to 60° C., in throughflow metallisingespecially in the range from 20° to 65° C. and most especially in therange from room temperature to 45° C. A coating with a copper content of0.1 to 40 g/m² can be applied in this way. In the coppering of wires,amounts of copper in particular in the range from 0.5 to 4 g/m² Cu canbe deposited in the throughflow method, and amounts in the range from 1to 20 g/m² Cu can be deposited in the dipping method. The layerthicknesses of the copper coating are generally up to 5 μm.Surprisingly, metallising can often still be carried out with adissolved iron content of the bath of up to 90 or even up to 110 g/lFe²⁺.

Before contact with the bath liquid the object to be metallised orpossibly the metallic object can first of all be cleaned under alkalineconditions and/or pickled under acidic conditions in a currentlessand/or electrolytic process and following this may also be rinsed withwater if necessary. After the currentless coppering or bronzing themetallised object may then be rinsed, optionally dried, optionallytreated with a passivating agent and optionally re-rinsed, optionallyannealed and, in the case of wires, optionally also be drawn at leastonce.

Normally coppering dipping baths can only handle an iron content of atmost only 80 g/l, in particular often only up to 60 g/l or even less, asa result of which the bath has to be replaced when the operating limitis reached, which in the case of throughflow plants is generally alreadyin the range from 15 to 30 g/l Fe²⁺ and in dipping plants is, dependingon the circumstances, only in the range from 60 to 80 g/l Fe²⁺ (alwaysas dissolved fraction), since the amount of deposited copper continuesto fall per unit time with the iron content of the bath. At least partof the bath then has to be discarded. Because of this low operatinglimit, which is quickly reached on account of the dissolution of theiron in the pickling of the metallic, generally steel object, to becoated, the bath volumes are often small. However in the case ofconventional coppering baths initial adverse effects, which lead to aninitial reduction of the layer weight per unit time (=deposition rate)and of the adherence of the copper-rich layer to the metallic substrate,already occur in some cases starting with dissolved iron contents of 5g/l Fe²⁺. In addition, for a good and efficient copper deposition it isnecessary for the object being metallised to be thoroughly cleaned, inparticular for organic contamination to be removed.

It appears possible in this way for the first time to be able to raisethe operating limit of the dipping bath to a range of at least 90 g/lFe²⁺ or even to a range of at least 110 g/l Fe²⁺. The dipping bath mayin some cases be able to operate possibly with an even higher dissolvediron content.

In addition it appears possible for the first time to be able to raisethe copper content of a concentrate or bath for currentless coppering orbronzing to concentrations far in excess of 25 g/l Cu, and to maintainthe content approximately at this order of magnitude. With the highercopper concentration of the bath it is also possible to establish ahigher deposition rate and to produce a high layer weight in a shortertime.

Finally, it appears possible for the first time to be able successfullyto develop a permanently storable concentrate or bath for currentlesscoppering or bronzing that in addition is also stable to freezing andthawing.

It was surprisingly found that the bath according to the invention doesnot lose its operational capability for coppering when iron contents inthe range from about 15 to 30 g/l Fe²⁺ referred to dissolved ironcontents are reached, as is at present normally the case with processesfor currentless coppering, but instead remains functional up to contentsof about 90 to 110 g/l Fe²⁺. Not only the copper deposition rate butalso the adhesion strength and gloss of the coating remain at a veryhigh quality up to this high operating limit. Since on account of theelectrochemical series the deposition of copper takes place by thedissolution of a less noble metal such as iron, iron ions rapidlyaccumulate in the bath. In this connection there is no ironprecipitation at the low pH value of far less than 2.5. If the dissolvediron content in the bath becomes higher, the voltage difference in thebath corresponding to the Nernst equation is no longer sufficiently highto cause the deposition of the nobler metal. With increasing ironcontent in the bath the copper deposition rate, the adherence of thecopper coating and the gloss of the coating all decrease. Obviously thenegative influence of the iron content is obviated to a large extent bythe nature of the complexing, in particular when using citrate. With thecementation of the copper the complex-forming agent becomes free againand can obviously complex the released Fe²⁺ ions. Corresponding to theNernst equation the copper concentration appears on account of thecomplexing to be at higher values in relation to the iron concentration.In this way the cathodic partial reaction could be displaced to valuescorresponding to nobler metals and lead to an increase in the copperingrate and to higher layer weights. Possibly the copper-citrate complex isalso less stable than the corresponding iron-citrate complex.

On account of the higher iron uptake of the bath the latter can be usedfor a multiple of the normal time without interruption, before the highiron content is rectified by discarding at least part of the bath. Thebath contents can then be replenished by adding further concentratecontaining all the components. Advantageously only the concentrate isused as replenishment solution.

It was surprisingly found that the adherence of the copper-rich coatingto the substrate does not drop sharply as is usual with a markedincrease in the layer weight of the copper-rich coating. In fact, adecrease in the layer weight from values of for example around about 2g/m² to about half or even a quarter of this value is normallyunavoidable, especially when coppering wires.

It was also found that a certain amount of brightening agent in the bathis necessary. However, an extra amount does not have any disadvantages,apart from the additional expense.

The concentrate according to the invention is easily transportable, canbe stored for at least six months, and is sufficiently stable tofreezing and thawing for transportation and storage.

The liquid concentrate has the following advantages compared to a solidconcentrate: 1. there are no problems or expenditure involved indissolving aggregates of the copper compounds such as for example coppersulfate (formation of lumps), which on account of the hygroscopicbehaviour of the powder clump together and cause problems when meteredin in an automated manner, 2. no halide has to be included, andaccordingly a neutral or slightly alkaline pH that is friendly to theskin can be adjusted, 3. there are no rapid uncontrolled secondaryreactions on account of the hygroscopic behaviour of the copper compoundand additives such as sodium chloride, 4. a concentration equilibriumover the length of the treatment bath is ensured sufficiently quicklysince the copper consumed in the bath has to be metered into the bathsubstantially continuously via the concentrate, 5. there are no problemsor extra expenditure involved in the metering of the concentrate sinceonly one vessel, a hose connection and a pump are required, 6. there isno extra expenditure in the transportation of highly acidic products, 7.the concentrate is a one-component product and 8. may, if necessary,already contain all the substances for the coppering or bronzing.Delivery of the liquid concentrate to other countries may therefore nowbe recommended, which is not the case with pulverulent concentrates.

The bath according to the invention and the metallising processaccording to the invention are particularly suitable for the currentlesscoppering or bronzing of wires or assemblies containing wires. The bathor process may be particularly successfully used for the metallising ofall types of wires, such as for example tyre inlay wire, paperclip wire,electrodes, mattress spring wire, welding wire, decorative wireapplications, etc. The metallising may however also be used as a formingaid or mould release agent, for example in flow pressing such as insteel slugs and for many other purposes. Such slugs can readily bedeformed in the coppered state at 300° to 350° C. in flow pressing.

EXAMPLES AND COMPARISON EXAMPLES

An initial bath was prepared based on water, anhydrous citric acid(complexing agent), sodium hydroxide, sulfuric acid and copperhydroxycarbonate (=basic copper carbonate), CuCO₃.Cu(OH)₂, whichcontained, as converted values, 31.3 g/l of sodium citrate, 55 g/l of96% sulfuric acid and 9.98 g/l of copper (comparison example 1). Thiscomposition also did not contain any brightening agent. Tap water wasused to prepare the bath. The pH value before the addition of thesulfuric acid was almost exactly 7, adjusted by adding the appropriateamount of sodium hydroxide. Sulfuric acid was added last, the pH valuethen being about 1.2. At least one liquid or solid additive was mixedwith this bath as necessary, and as brightening agent for all theexamples according to the invention there was added a product based on apolymeric reaction product of dimethylamino-propylamine andepichlorohydrin (Examples 2 ff. and comparison examples).

Wire rods with a carbon content of 0.65 wt. % and 5.5 mm diameter weredipped in these baths, for example for 2 minutes at 30° C. (Table 1).The dipping time is calculated from the start of dipping up to theremoval of the rods from the bath. In addition the coppering wasinvestigated with regard to the dependence on time and temperature viathe copper layer weight obtained in each case by dipping and, parallelthereto, in a throughflow unit with a bath composition according toExample 10. Following this the copper layer weight was determined as afunction of the dissolved iron-II ion content—simulated in a dippingbath at 30° C. or for a throughflow unit at 50° C.—for a bathcomposition according to Example 10. The results are summarised inTables 1-3.

Comparison examples 1 to 5 and examples 1 to 10 ACCORDING to theinvention:

The additives specified in Table 1 were added to the initial bathmentioned above. The wire rods were dipped in this bath under thespecified standard conditions. The determined properties are shown inTable 1.

TABLE 1 Composition and properties of the various baths complementingthe data in comparison example 1, and properties of the coppered wires;additions in g/l unless otherwise specified. VB 1 VB 2 VB 3 VB 4 VB 5 B1 B 2 B 3 B 4 B 5 B 6 B 7 B 8 B 9 B 10 Brightening agent 0 0 0 0 0 0.010.1 1 15 0.1 0.1 0.1 0.1 0.1 0.1 NaCl 0 5 0 0 0 5 5 5 5 1 0 0 0 1 0 NaBr0 0 5 0 0 0 0 0 0 0 5 0 0 1 0 HCl 37% 0 0 0 2 ml 0 0 0 0 0 0 0 2 ml 0 00 MgSO₄ 0 0 0 0 2 0 0 0 0 0 0 0 2 2 0 Adherence − − − − − + ++ ++ ++++ + ++ + ++ ++ Gloss matt matt matt matt matt + ++ ++ ++ ++ ++ ++ ++ ++++ Homogeneity inhom. inhom. inhom. inhom. inhom. + ++ ++ ++ ++ ++ ++ ++++ ++ Colour d'br d'br d'br d'br d'br Cu-f Cu-f Cu-f Cu-f Cu-f Cu-f Cu-fCu-f Cu-f Cu-f Layer * * * * * + ++ ++ ++ ++ ++ ++ ++ ++ ++

In all the comparison examples the adherence was extremely low since thecopper coat could already be wiped off with a damp linen cloth. Thedegree of inhomogeneity or homogeneity is indicated inter alia by thenumber of “stars”. “inhom.” denotes an inhomogeneous coppering, while“*” denotes a non-closed coating. The colour of the copper coat was darkbrown (d′br in the comparison examples) instead of the typical coppercolour (Cu-f).

It was surprisingly found that even a comparatively very high bromidecontent did not have an interfering effect. All the copper coatingsobtained according to the invention were smooth, closed, shiny and of atypical copper colour and adhered well. However, in this series ofexperiments it was found that the adherence of the copper coat that hadbeen produced in the presence of chloride ions was even slightly betterthan without a content of chloride ions.

TABLE 2 Coppering behaviour depending on temperature and time in a bathbased on Example 10, and properties of the coppered wires. SG = layerweight of the copper coat. Examples 11-24 relate to dipping and Examples25-36 relate to the throughflow process. Example B 11 B 12 B 13 B 14 B15 B 16 B 17 B 18 B 19 B 20 B 21 B 22 B 23 B 24 Temp. in ° C. 30 30 3030 40 40 40 50 50 50 50 60 60 60 Time in min. 2 5 10 15 2 5 10 1 2 5 102 5 10 Time in sec. Dipping SG in g/m² 4.0 8.3 13.4 17.4 8.0 13.5 21.64.6 7.8 18.8 22.9 5.4 12.6 21.0 Adherence ++ ++ ++ ++ ++ ++ ++ ++ ++ ++++ ++ ++ ++ Gloss ++ ++ ++ ++ ++ ++ ++ ++ ++ ++ ++ ++ ++ ++ Homogeneity++ ++ ++ ++ ++ ++ ++ ++ ++ ++ ++ ++ ++ ++ Colour Cu-f Cu-f Cu-f Cu-fCu-f Cu-f Cu-f Cu-f Cu-f Cu-f Cu-f Cu-f Cu-f Cu-f Layer ++ ++ ++ ++ ++++ ++ ++ ++ ++ ++ ++ ++ ++ Example B 25 B 26 B 27 B 28 B 29 B 30 B 31 B32 B 33 B 34 B 35 B 36 Temp. in ° C. 40 40 40 40 50 50 50 50 60 60 60 60Time in min. Throughflow Process Time in sec. 7.5 15 30 60 7.5 15 30 607.5 15 30 60 SG in g/m² 0.8 1.9 4.3 7.1 1.7 2.5 6.0 9.4 2.3 2.7 6.6 11.6Adherence ++ ++ ++ ++ ++ ++ ++ ++ ++ ++ ++ ++ Gloss ++ ++ ++ ++ ++ ++ ++++ ++ ++ ++ ++ Homogeneity ++ ++ ++ ++ ++ ++ ++ ++ ++ ++ ++ ++ ColourCu-f Cu-f Cu-f Cu-f Cu-f Cu-f Cu-f Cu-f Cu-f Cu-f Cu-f Cu-f Layer ++ ++++ ++ ++ ++ ++ ++ ++ ++ ++ ++

Table 3: Coppering behaviour depending on temperature, time anddissolved Fe²⁺ content in a bath based on Example 10, and properties ofthe coppered wires. SG=layer weight of the copper coat. Examples 41-55relate to dipping and Examples 56-67 relate to the throughflow process.

TABLE 3 Coppering behaviour depending on temperature, time and dissolvedFe²⁺ content in a bath based on Example 10, and properties of thecoppered wires. SG = layer weight of the copper coat. Examples 41-55relate to dipping and Examples 56-67 relate to the throughflow process.Example B 41 B 42 B 43 B 44 B 45 B 46 B 47 B 48 B 49 Temp. in ° C. 30°C. - Simulation of dipping Time in min. 2 5 10 2 5 10 2 5 10 SG in g/m²3.2 9.4 15.1 3.8 11.2 18.7 5.4 10.2 17.1 Fe²⁺ in g/l 0 0 0 2 2 2 5 5 5Adherence ++ ++ ++ ++ ++ ++ ++ ++ ++ Gloss ++ ++ ++ ++ ++ ++ ++ ++ ++Homogeneity ++ ++ ++ ++ ++ ++ ++ ++ ++ Colour Cu-f Cu-f Cu-f Cu-f Cu-fCu-f Cu-f Cu-f Cu-f Layer ++ ++ ++ ++ ++ ++ ++ ++ ++ Example B 50 B 51 B52 B 53 B 54 B 55 B 56 B 57 B 58 Temp. in ° C. 30° C. - Simulation ofdipping 50° C. - Throughflow process Time in min. 2 5 10 2 5 10 Time insec. 7.5 15 30 SG in g/m² 3.8 6.7 12.3 4.4 4.5 12.3 1.7 2.5 6.0 Fe²⁺ ing/l 10 10 10 20 20 20 0 0 0 Adherence ++ ++ ++ ++ ++ ++ ++ ++ ++ Gloss++ ++ ++ ++ ++ ++ ++ ++ ++ Homogeneity ++ ++ ++ ++ ++ ++ ++ ++ ++ ColourCu-f Cu-f Cu-f Cu-f Cu-f Cu-f Cu-f Cu-f Cu-f Layer ++ ++ ++ ++ ++ ++ ++++ ++ Example B 59 B 60 B 61 B 62 B 63 B 64 B 65 B 66 B 67 Temp. in ° C.50° C. - Simulation of the throughflow process Time in sec. 60 7.5 15 3060 7.5 15 30 60 SG in g/m² 9.4 1.5 2.1 2.6 6.7 1.6 2.1 3.1 4.8 Fe²⁺ ing/l 0 10 10 10 10 20 20 20 20 Adherence ++ ++ ++ ++ ++ ++ ++ ++ ++ Gloss++ ++ ++ ++ ++ ++ ++ ++ ++ Homogeneity ++ ++ ++ ++ ++ ++ ++ ++ ++ ColourCu-f Cu-f Cu-f Cu-f Cu-f Cu-f Cu-f Cu-f Cu-f Layer ++ ++ ++ ++ ++ ++ ++++ ++

The adherence was tested in all experiments by vigorously wiping thecoppered wires with a damp linen cloth. In this connection, nosignificant differences in adherence were found in the examplesaccording to the invention. All the copperings according to theinvention were completely satisfactory. Furthermore, with variations inthe compositions and/or treatment conditions there was no deteriorationof the adherence with particularly high temperatures and particularlylong coppering times, as sometimes occurs in conventional copperingbaths under these operating conditions. At a temperature of 30° C. andwith a dipping time of up to 4 minutes the gloss is slightly less goodthan in the remaining dipped samples. The same also applies as regardsthe simulation of the throughflow units. The gloss in principleincreases slightly with temperature and also slightly with dipping timeor throughflow time, though the homogeneity may, depending on thecircumstances, be slightly adversely affected at particularly hightemperatures and particularly long coppering times, for example due tominute black spots. Apart from this the homogeneity of all samplesaccording to the invention was at least as good, if not even in somecases even more uniform, than in conventional currentless coppering. Allsamples exhibited the typical copper colour in the same way. A closed,smooth, high-quality copper layer was always produced.

In the experiments according to the invention relating to copperdeposition as a function of the iron content, a uniformly high qualityas regards adherence, homogeneity, copper coat and deposition qualitywas found in all samples. Only the gloss of the samples exhibited aslight deterioration in some cases with iron contents of 20 g/l andabove, particularly with longer coppering times. With the samples thathad been coppered on the one hand by dipping, and on the other hand bythe throughflow process with 90 or 110 g/l of Fe²⁺ dissolved in thebath, the gloss was noticeably less good but was always still adequate,although the coppering was satisfactory apart from the bath behaviourand the other properties. The gloss is in any case not so important inthe coppering of wires since the wires always in addition have to bedrawn after the coppering and the coppering layer is thereby improvedstill further as regards gloss.

1. An aqueous composition comprising water; copper hydroxycarbonate; acopper complex-forming agent; and at least one complexed water-solubleor water-dispersible copper complex formed by complexing of said coppercomplex forming agent and a copper ion from said copperhydroxycarbonate.
 2. The aqueous composition according to claim 1,wherein at least 40 wt.% of the total amount of copper from said copperhydroxycarbonate is complexed.
 3. An aqueous composition according toclaim 1, wherein the complexing agent is selected from the groupconsisting of monohydroxycarboxylic, acid, dihydroxycarboxylic acid,trihydroxycarboxylic acid, polyhydroxycarboxylic acid, phosphonic acid,diphosphonic acid and derivatives thereof.
 4. An aqueous compositionaccording to claim 1 that is stable to freezing and thawing down to atemperature of at least −8° C.
 5. An aqueous composition according toclaim 1, having a copper content in the range from 3 to 200 g/l Cu. 6.The aqueous composition according to claim 1 adjusted to a pH value inthe range from 4 to
 11. 7. The aqueous composition of claim 1 furthercomprising at least one brightening agent.
 8. The aqueous composition ofclaim 1 further comprising a residue of basic copper carbonate.
 9. Theaqueous composition of claim 1 having a pH value of less than 2.5. 10.The aqueous composition according to claim 9 wherein at least 40 wt.% ofthe contained copper compounds are complexed.
 11. The aqueouscomposition according to claim 9 having a copper content in the rangefrom 0.05 to 120 g/l.
 12. The aqueous composition according to claim 9,further comprising iron wherein the iron content is up to at least 90g/l Fe²⁺.
 13. The aqueous composition according to claim 9, furthercomprising iron wherein the iron content is up to at least 110 g/l Fe²⁺.14. The aqueous composition according to claim 9 wherein the coppercomplex forming agent is selected from the group consisting ofmonohydroxycarboxylic acid, dihydroxycarboxylic acid,trihydroxycarboxylic acid, polyhydroxycarboxylic acid, phosphonic acid,diphosphonic acid or a derivative thereof.